An inversion layer transistor utilizing a semiconductor base in conjunction with a metal emitter and a metal collector is known in the prior art. In particular, Mead U.S. Pat. No. 3,289,052 discloses such a transistor in which a P type indium arsenide base separates metallic emitter and collector elements. Since indium arsenide has the property of having its Fermi level pinned in the conduction band near the semiconductor-metal inferfaces, an accumulation of electrons at the interfaces create N type inversion layers thereat.
It is recognized that the highly inverted layers form barriers which are assymmetrically conducting, and the base-emitter barrier is lower for the passage of electrons from the metal to the base than for the passage of holes in the opposite direction. Thus, when the base-emitter interface is forward biased, the large number of electrons at the interface are projected into and across the base, thus providing a high emitter efficiency transistor having excellent high frequency characteristics.
Notwithstanding the advantageous speed of the above-described prior art transistor, to applicants knowledge it has not been developed commercially. It is believed that an important factor in the lack of commercial interest in the prior art transistor is the incompatability of the metal elements which it requires with current semiconductor fabrication technology.
In distinction thereto, the present invention provides an inversion layer transistor which retains all the advantages of the prior art device, but which, in addition, is made entirely of semiconductor material. Thus, unlike the prior art transistor, the transistor of the present invention may be epitaxially grown on semiconductor substrates, and therefore may be incorporated into integrated circuitry, such as for example very large scale integrated circuitry (VLSIC). Thus all of the ease, convenience and flexibility of working with semiconductor materials as well as the highly developed fabrication techniques associated therewith attach to the present invention. Further, better product uniformity and material quality is obtained with the present transistor and integrated circuits incorporating it, than with the metal-emitter transistor of the prior art.